Such atomic absorption spectrometer and such method are known in the prior art.
FIG. 5 schematically shows an atomic absorption spectrometer 500 in accordance with the prior art. The atomic absorption spectrometer 500 comprises a measuring light path 510 and a reference light path 520. Further, the atomic absorption spectrometer 500 is provided with a light source 550 emitting a line radiation corresponding to an element to be detected, said element being contained in a sample to be examined.
The light emitted by the light source is coupled, by a chopper means 590, into either the measuring light path 510 of the reference light path 520. The coupling is in accordance with the position of the elements being provided in the chopper means (not shown).
In FIG. 5a, the light path is shown for a first position of the elements of the chopper means 590. In this position, the light emitted from the light source is coupled into the measuring light path 510. Accordingly, the reference light path 520 is represented by a dashed line.
The light emitted from the light source travels on the measuring light path 510 through an atomization means 560 in which the sample to be examined is atomized. In FIG. 5, the atomization means 560 is only shown schematically. In dependency on the sample matrix and the element contained in the sample, all atomization means known in the field of atomic absorption spectroscopy, as for example atomization furnace, flame, cold vapor cell and the like, can be used.
After passing through the atomization means 560, the radiation impinges on a detector device 530, for measuring the intensity of the radiation.
In FIG. 5b, the light path is shown for a second position of the elements of the chopper means 590. In this position, the light emitted from the light source is coupled into the reference light path 520. In accordance with FIG. 5a, the measuring light path 510 is shown in dashed line in FIG. 5b.
Using the reference light path 510, the line radiation emitted from the light source impinges directly onto the detector 530 for measuring the intensity of the radiation.
Beside the above described components, the atomic absorption spectrometer 500 comprises optical elements 511 and 521, for example, mirrors and/or lenses. These optical elements are, if need be, for focusing and redirecting the light paths.
In the following, a method for performing a double-beam atomic absorption spectroscopy with the atomic absorption spectrometer of FIG. 5 will be described. With this, reference is made to FIG. 14, representing a time sequence of the method.
After the sample has been atomized in the atomization means 560, line radiation from the light source is coupled in accordance with the respective position of the elements of the chopper means (see FIG. 5A), into the measuring light path 510 for a predetermined time T.sub.T during a first phase P of a measuring cycle C, and the intensity of the radiation passed through the measuring light path 510 is measured in the detector device 530.
After completion of this measurement, radiation emitted by the light source is coupled for a predetermined time T.sub.R into the reference light path due to the respective position of the chopper means (see FIG. 5b). The intensity of the radiation path through the reference light path is detected in the detector device 430.
Finally, the radiation absorbed by the atomized sample is determined from the intensity of the radiation passed through the measuring light path and the intensity passed through the reference light path.
The measuring cycle shown in FIG. 14 is repeatedly performed in order to improve the statistics, in particular, if the atomic absorption is constant over a range which is larger compared to the measuring time. The case of these slowly running processes is particularly seen in the absorption with a flame or a cold vapor cell.
For fast running processes, as for example the atomization in an atomization furnace, the measurements can be, instead of averaging, time dependently recorded. Thus, with the above described spectrometer and respective methods, it is possible to perform an atomic absorption spectroscopy with time resolution.
The disadvantage of the above described spectrometer and the method is the loss of measuring time due to performing the reference measurement, i.e. the second phase R of the measuring cycle T. This is particularly critical in an atomization with an atomization furnace, since the available measuring time is generally very short.